Reducing agent aqueous solution mixing device and exhaust gas post-treatment device

ABSTRACT

A reducing agent aqueous solution mixing device includes an exhaust pipe, an injector, an inner pipe and a tubular guide member. The exhaust pipe includes an elbow part having a curved portion, and a linear part disposed downstream of the elbow part. The injector is disposed outside of the curved portion, and injects a reducing agent aqueous solution into the elbow part towards the linear part. The inner pipe is disposed downstream of the injector within the exhaust pipe. The inner pipe has an inlet portion opening facing the injector and an outer peripheral surface spaced apart from the inner wall of the linear part. The inner pipe allows the exhaust gas to flow through the inside of the inner pipe and along the outer periphery of the inner pipe. The tubular guide member directs the reducing agent aqueous solution injected from the injector to the inner pipe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2011-285451 filed on Dec. 27, 2011, the disclosure of which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a reducing agent aqueous solution mixing device, particularly to, a reducing agent aqueous solution mixing device for adding a reducing agent aqueous solution to exhaust gas, which is disposed between a filter for trapping particulate substance in the exhaust gas and a reducing catalyst unit for reducing and purifying nitrogen oxide in the exhaust gas while being disposed parallel to the filter. Further, the present invention relates to an exhaust gas post-treatment device including the aforementioned reducing agent aqueous solution mixing device.

BACKGROUND ART

The exhaust gas of engines contains nitrogen oxide (NOx). An exhaust gas post-treatment device is disposed at an intermediate position in an exhaust path for inhibiting emission of the nitrogen oxide into the air. The exhaust gas post-treatment device includes a filter for trapping particulate substance in the exhaust gas, a urea aqueous solution mixing device disposed on the exhaust downstream side of the filter in order to add a urea aqueous solution to the exhaust gas, and a reducing catalyst disposed on the further downstream side of the mixing device in order to reduce and purify nitrogen oxide in the exhaust gas.

The urea aqueous solution mixing device in the aforementioned exhaust gas post-treatment device includes an injector that injects a urea aqueous solution as a reducing agent into an exhaust pipe. The urea aqueous solution, injected into the exhaust pipe from the injector, is mixed with the exhaust gas and is supplied to the reducing catalyst on the exhaust downstream side. Here, firstly, the urea aqueous solution is thermally decomposed by the exhaust gas and ammonia is thereby obtained. Then, in the reducing catalyst, the ammonia is used as a reducing agent and the nitrogen oxide in the exhaust gas is reduced and purified.

In such device, a sufficient reaction time is required for thermally decomposing the urea aqueous solution and thereby Obtaining ammonia. To achieve this, it is required to reliably produce a long distance between the injector and the reducing catalyst. When the distance is short, the urea aqueous solution injected within the exhaust pipe is not sufficiently mixed with the exhaust gas, while partially attaching as droplets to the inner wall of the exhaust pipe cooled by the external air. The urea aqueous solution, thus attached to the inner wall of the exhaust pipe, is not easily decomposed. Therefore, there may be deficiency in ammonia to be supplied to the reducing catalyst. Further, the urea aqueous solution, changed into droplets on the inner wall of the exhaust pipe, may be crystallized and deposited on the inner wall.

In view of the above, as described in Publication of Japanese Translation of PCT International Application No. JP-A-2008-509328 and WO2006/025110 A1, devices have been provided that a double-nested pipe structure is produced by disposing an inner pipe within an exhaust pipe on the exhaust downstream side of an injector and a urea aqueous solution is configured to be injected into the inner pipe. The exhaust gas herein flows around the outer peripheral part of the inner pipe. Therefore, the inner pipe is heated by the exhaust gas, and accordingly, the urea aqueous solution can be inhibited from attaching as droplets to the inner wall of the inner pipe,

SUMMARY

As described in JP-A-2008-509328 and WO2006/025110 A1, a type of injector, mixing and injecting the air and the urea aqueous solution, is required for injecting the urea aqueous solution in a direction along an exhaust stream in the center part of the inner pipe.

Now, in recent years, abolishment of compressors as air sources has been demanded in the field of work vehicles. Therefore, injectors often used are of so-called an airless type that directly injects only the urea aqueous solution without mixing the air therewith. As described in JP-A-2008-509328 and WO2006/025110 A1, such airless type injectors cannot inject the urea aqueous solution to the center part of the inner pipe along the exhaust stream.

In view of the above, in using an airless type injector, it can be assumed that an elbow pipe is disposed on the exhaust upstream side of a double nested pipe structure in which an inner pipe is disposed, and an injector is disposed outside a curved portion of the elbow pipe. In such arrangement, the injection outlet of the injector is opposed to the inlet-portion opening of the inner pipe, and therefore, the urea aqueous solution can be injected from the injector towards the inner pipe along the exhaust stream.

However, when the injector is disposed at the curved portion of the elbow pipe, the injection outlet of the injector and the inlet portion of the inner pipe are separated away from each other. Therefore, it is difficult to efficiently cause the urea aqueous solution injected from the injector to flow into the inner pipe. Further, when such structure is employed, the urea aqueous solution injected from the injector is supposed to be pushed towards the inner wall of the elbow pipe by the impetus of the exhaust gas flowing thereto from the upstream side of the elbow pipe. The elbow pipe is being cooled by the external air. Therefore, the urea aqueous solution, colliding against the inner wall, may be attached as droplets to the inner wall of the elbow pipe. It is an object of the present invention to efficiently direct the reducing agent aqueous solution injected from an injector to an inner pipe, and further, to inhibit the reducing agent aqueous solution from attaching to the inner wall of an injector attached portion of an exhaust pipe in a reducing agent aqueous solution mixing device using the injector for directly injecting only the reducing agent aqueous solution such as urea aqueous solution into the exhaust pipe.

A reducing agent aqueous solution mixing device according to a first aspect is a device for adding a reducing agent aqueous solution to an exhaust gas, which is disposed between a filter trapping particulate substance in the exhaust gas and a reducing catalyst unit reducing and purifying nitrogen oxide in the exhaust gas, and includes an exhaust pipe, an injector, an inner pipe and a tubular guide member. The exhaust pipe includes: an elbow part having a curved portion; and a linear part disposed on an exhaust downstream side of the elbow part. The injector is disposed outside the curved portion of the elbow part, and injects only the reducing agent aqueous solution of an air unmixed state into the elbow part towards the linear part. The inner pipe is disposed on an exhaust downstream side of the injector while an exhaust upstream side inlet portion opening thereof faces the injector and an outer peripheral surface thereof is disposed at an interval away from an inner wall of the linear part, and allows the exhaust gas to flow through an inside thereof and an outer periphery thereof. The tubular guide member for directs the reducing agent aqueous solution injected from the injector to the inner pipe.

In the device, the exhaust gas, flowing from the upstream side, flows via the elbow part into the linear part in which the inner pipe is disposed in the elbow part, the reducing agent aqueous solution is injected from the injector towards the inner pipe. The injected reducing agent aqueous solution is directed to the inner pipe while being guided by the guide member.

Here, the reducing agent aqueous solution, injected from the injector, can be efficiently directed to the inner pipe. Therefore, the reducing agent aqueous solution can be inhibited from attaching to the inner wall of the elbow part.

A reducing agent aqueous solution mixing device according to a second aspect relates to the device of the first aspect, and wherein the guide member is a mixing pipe that is disposed for enclosing a surrounding of the reducing agent aqueous solution to be injected from the injector and has a plurality of openings on an outer peripheral surface thereof.

Here, the exhaust gas, flowing to the elbow part, flows into the mixing pipe through the openings on the outer peripheral surface of the mixing pipe. Inside the mixing pipe, the reducing agent aqueous solution is injected from the injector. Therefore, the exhaust gas and the reducing agent aqueous solution are mixed inside the mixing pipe. The exhaust gas and the reducing agent aqueous solution, mixed in the mixing pipe, flow into the downstream inner pipe. The inner pipe is being heated by means of the exhaust gas flowing through the outer periphery thereof. Even when attached to the inner wall of the inner pipe, the reducing agent aqueous solution is evaporated and changed into ammonia. Therefore, the reducing agent aqueous solution can be inhibited from attaching to the inner wall of the exhaust pipe and that of the inner pipe.

A reducing agent aqueous solution mixing device according to a third aspect relates to the device of the second aspect, and wherein the mixing pipe is disposed for producing an interval between an exhaust stream downstream side outlet portion thereof and the inner wall of the exhaust pipe. Further, a flow section is formed between the outlet portion and the inner wall of the exhaust pipe in order to direct the exhaust gas residing in the outer periphery of the mixing pipe to the inner pipe.

When members such as the mixing pipe and the inner pipe are herein disposed inside the exhaust pipe, it is required to prevent increase in flow path resistance. If the flow path resistance is increased when the exhaust gas passes through the mixing pipe, the back pressure of the engine is increased, and thereby; results in deterioration in fuel consumption.

In view of the above, according to the present third aspect, an interval is reliably produced between the outlet portion of the mixing pipe and the inner wall of the exhaust pipe, and the flow section is formed for directing the exhaust gas residing in the outer periphery of the mixing pipe to the inner pipe. With such structure, the flow path resistance in the exhaust pipe is reduced and the back pressure of the engine is inhibited. Accordingly, deterioration in fuel consumption can be prevented.

A reducing agent aqueous solution mixing device according to a fourth aspect relates to the device of the third aspect, and wherein the mixing pipe is supported at an end portion thereof disposed oppositely to the outlet portion by an elbow part wall facing the linear part.

In such support structure of the mixing pipe, the vicinity of the outlet portion of the mixing pipe is not required to be supported with respect to the exhaust pipe. In other words, it is not required to dispose a member fur obstructing the flow of the exhaust gas in the flow section between the outlet portion of the mixing pipe and the exhaust pipe inner wall. Therefore, the flow path resistance in the exhaust pipe can be reduced.

A reducing agent aqueous solution mixing device according to a fifth aspect relates to the device of any of the second to fourth aspects, and wherein the plural openings of the mixing pipe are formed only in a partial angular range of the mixing pipe in a circumferential direction.

Here, the openings of the mixing pipe are formed only in a part of the outer peripheral surface of the mixing pipe. Therefore, the exhaust gas, inhaled inside the mixing pipe through the openings, is supposed to form a constant stream. Therefore, the flow of the exhaust gas promotes the mixture of the exhaust gas and the reducing agent aqueous solution and the decomposition of the reducing agent aqueous solution.

A reducing agent aqueous solution mixing device according to a six aspect relates to the device of the fifth aspect, and Wherein the plural openings of the mixing pipe are thrilled either only in first and third regions or second and fourth regions where an outer circumference of the mixing pipe is equally divided in four sequentially aligned regions consisting of the first region, the second region, the third region and the fourth region at 90-degree intervals in the circumferential direction.

Here, similarly to the fifth aspect, the exhaust gas inside the mixing pipe forms a constant stream. Therefore, the mixture of the exhaust gas and the reducing agent aqueous solution and the decomposition of the reducing agent aqueous solution are promoted.

A reducing agent aqueous solution mixing device according to a seventh aspect relates to the device of any of the second to sixth aspects, and wherein the inlet portion of the inner pipe has an inner diameter greater than an inner diameter of the outlet portion of the mixing pipe.

Here, the exhaust gas and the reducing agent aqueous solution, mixed inside the mixing pipe, smoothly flow into the timer pipe. Further, the exhaust gas, having flown through the flow section in the outer periphery of the mixing pipe, also easily gets to flow into the inner pipe.

A reducing agent aqueous solution mixing device according to an eighth aspect relates to the device of the seventh aspect, and wherein the mixing pipe and the timer pipe are disposed so that an outlet portion opening of the mixing pipe and an inlet portion opening of the inner pipe encompass an injection angular range of the injector.

Here, the outlet portion opening of the mixing pipe is formed wider than the diffusion range of the injected reducing agent aqueous solution. The injected reducing agent aqueous solution is thereby prevented from directly colliding against the inner wall of the mixing pipe. Therefore, the reducing agent aqueous solution can be inhibited from attaching as droplets to the inner wall of the mixing pipe. Further, the opening of the inlet portion of the inner pipe is wider than the diffusion range of the reducing agent aqueous solution. The injected reducing agent aqueous solution can be thereby efficiently inhaled into the inner pipe.

A reducing agent aqueous solution mixing device according to a ninth aspect relates to the device of any of the first to eighth aspects, and further includes a support member including support portions for supporting a plurality of circumferential portions of an outer peripheral part of the inner pipe with respect to the exhaust pipe at a single position in a direction arranged along the exhaust stream. Further, except for the support portions, other regions between the support member and an outer peripheral surface of the inner pipe allow the exhaust gas to flow therethrough, and the inner pipe has no opening funned on the outer peripheral surface thereof.

Here, the outer peripheral part of the inner pipe is supported with respect to the exhaust pipe by the support portions of the support member. Further, the exhaust gas smoothly flows through the other regions except fur the support portions in the outer periphery of the inner pipe. Yet thriller, the inner pipe has no opening formed on the outer peripheral surface thereof. Therefore, a sufficient amount of exhaust gas is supposed to flow through the outer periphery of the inner pipe. The inner pipe is thereby efficiently heated.

A reducing agent aqueous solution mixing device according to a tenth aspect relates to the device of any of the first to eighth aspects, and further includes a support member that supports an outlet portion of the inner pipe with respect to the exhaust pipe and restricts a flow of the exhaust gas residing between the outer peripheral surface of the inner pipe and the inner wall of the exhaust pipe. Further the outlet portion of the inner pipe has a plurality of openings formed on an outer peripheral surface thereof.

Here, the support member restricts the flow of the exhaust gas at the outlet portion of the inner pipe. Therefore, the exhaust gas in the outer periphery of the inner pipe flows into the inner pipe through the openings of the outer peripheral surface of the inner pipe in the vicinity of the outlet portion. Therefore, the exhaust gas and the reducing agent aqueous solution are further mixed at the outlet portion of the inner pipe. Therefore, the decomposition of the reducing agent aqueous solution is further promoted.

The reducing agent aqueous solution mixing device according to an eleventh aspect relates to the device of any of the second to tenth aspects, and wherein the mixing pipe and the inner pipe are coaxially disposed.

Here, the exhaust gas and the reducing agent aqueous solution, mixed in the mixing pipe, smoothly flow into the inner pipe.

An exhaust gas post-treatment device according to a twelfth aspect includes: a filter trapping particulate substance in an exhaust gas; the reducing agent aqueous solution mixing device recited in any of the first to eleventh inventions disposed parallel to the filter on an exhaust downstream side of the filter; and a reducing catalyst unit that is disposed on the exhaust downstream side of the reducing agent aqueous solution mixing device and reduces and purifies nitrogen oxide in the exhaust gas.

An exhaust gas post-treatment device according to a thirteenth aspect relates to the device of the twelfth aspect, and wherein the reducing catalyst unit is disposed parallel to the reducing agent aqueous solution mixing device.

According to the present invention as described above, in the reducing agent aqueous solution mixing device using the injector directly injecting only the reducing agent aqueous solution into the exhaust pipe, it is possible to efficiently direct the reducing agent aqueous solution injected from the injector to the inner pipe, and further, to inhibit the reducing agent aqueous solution from attaching to the inner wall of an injector attached portion of the exhaust pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of an exhaust gas post-treatment device according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional structural diagram of a urea aqueous solution mixing device according to an exemplary embodiment of the present invention.

FIG. 3 is a front view of a flange.

FIG. 4 is a diagram illustrating a mixing pipe and an attachment structure thereof.

FIG. 5 is a right side view of FIG. 4.

FIG. 6 is a diagram for explaining an injection angle of an injector, a mixing pipe and an arrangement of an inner pipe.

FIG. 7 is a diagram illustrating the flow of exhaust gas within an exhaust pipe.

FIG. 8 is a diagram illustrating the flow of the exhaust gas within the mixing pipe.

FIG. 9 is a diagram, corresponding to FIG. 2, according to another exemplary embodiment of the present invention.

FIG. 10 is a diagram illustrating a mixing pipe according to yet another exemplary embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS Overall Structure

FIG. 1 is a structural diagram of an exhaust gas post-treatment device 1 according to an exemplary embodiment of the present invention. The exhaust gas post-treatment device 1 includes a diesel particulate filter (hereinafter referred to as “DPF”) 1A, a urea aqueous solution mixing device 1B and a nitrogen oxide reducing catalyst unit (hereinafter referred to as “SCR”) 1C, which are sequentially disposed from an exhaust upstream side (hereinafter simply referred to as “an upstream side”). Each of the devices is disposed in an intermediate portion of an exhaust pipe through which exhaust gas, discharged from a diesel engine (not illustrated in the figure) through an exhaust manifold, flows.

The DPF 1A serves to trap particulate substance in the exhaust gas and is accommodated within a case 4A.

The urea aqueous solution mixing device 1B serves to add a urea aqueous solution as a reducing agent to the exhaust gas. The added urea aqueous solution is hydrolyzed and changed into ammonia. The ammonia, together with the exhaust gas, is supplied to the SCR 1C through a connection pipe 2. It should be noted that the urea aqueous solution mixing device 1B will be explained below in detail.

In the SCR 1C, the ammonia from the urea aqueous solution mixing device 1B is used as a reducing agent and nitrogen oxide in the exhaust gas is reduced and purified. The SCR 1C is accommodated within a case 4C.

The case 4A accommodating the DPF 1A, the urea aqueous solution mixing device 1B, and the case 4C accommodating the SCR 1C are respectively disposed in parallel Further, the exhaust downstream side (hereinafter simply referred to as “a downstream side”) end portion of the case 4A and the upstream side end portion of the urea aqueous solution mixing device 1B are coupled, while the downstream side end portion of the urea aqueous solution mixing device 1B and the upstream side end portion of the case 4C are connected through the curved connection pipe 2.

As described above, the case 4A, the urea aqueous solution mixing device 1B and the case 4C are disposed in an S-shape, and thereby, an entirely compact exhaust gas post-treatment device is formed. It should be noted that an oxidative catalyst unit may be disposed on the upstream side of the DPF 1A within the case 4A in order to execute an oxidative treatment for unburnt fuel in the exhaust gas. Further, an ammonia reducing catalyst unit may be disposed on the downstream side of the SCR 1C within the case 4C in order to execute an oxidative treatment for surplus ammonia,

Urea Aqueous Solution Mixing Device

FIG. 2 illustrates the structure of the urea aqueous solution mixing device 1B according to an exemplary embodiment of the present invention. As described above, the urea aqueous solution mixing device 1B is disposed between the DPF 1A and the SCR 1C. It should be noted that the illustration in FIG. 1 also includes the connection pipe 2 connected to the downstream side of the urea aqueous solution mixing device 1B.

The urea aqueous solution mixing device 1B includes an exhaust pipe 4B, an injector 5 for injecting a urea aqueous solution, a mixing pipe 6 and an inner pipe 7.

Exhaust Pipe

The exhaust pipe 4B includes an elbow part 10 disposed on the exhaust upstream side (hereinafter simply referred to as “an upstream side”) and a linear part 11 disposed on the downstream side of the elbow part 10. The elbow part 10 and the linear part 11 are both cylindrically formed.

The elbow part 10 is a connection pipe for causing the exhaust gas, flown thereto in an x-direction (a direction that the exhaust gas flows on the upstream side) depicted in FIG. 2, to flow in a y-direction perpendicular to the x-direction. The elbow part 10 has a curved portion 10 a. An attachment portion 10 b, formed by a plane arranged along the x-direction, is disposed on the outer part of the curved portion 10 a. In other words, the attachment portion 10 b faces the inlet-portion opening of the linear part 11. Further, a connection flanged portion 10 c is formed on the upstream-side end portion of the elbow part 10, whereas a connection flanged portion 10 d is formed on the downstream-side end portion of the elbow part 10. It should be noted that apertures into which connection bolts are fitted are formed in the flanged portions 10 c and 10 d.

The linear part 11 is a linear pipe extended along the y-direction. A connection-and-support flange (support member) 12 is welded to the upstream-side end portion of the linear part 11, whereas an annular adaptor 13 is welded to the downstream-side end portion of the linear part 11 in order to connect the connection pipe 2.

As illustrated in FIG. 3, the flange 12 is a rectangular plate member. Apertures 12 a, into which bolts are fitted for connecting the flange 12 to the flanged portion 10 d of the elbow part 10, are formed in four corner portions of the flange 12. Further, an aperture 12 b, having the same diameter as the inner diameter of the linear part 11, is formed in the center part of the flange 12. Yet further, four support protrusions 12 c, formed in the same shape, are disposed in the aperture 12 b for protruding from the outer peripheral side towards the center part. The four support protrusions 12 c are disposed at equal angular intervals.

The elbow part 10 and the linear part 11 are coupled by fixing such flange 12 to the flanged portion 10 d of the elbow part 10 by means of the bolts.

Injector

The injector 5 is attached, together with the mixing pipe 6, to the attachment portion 10 b on the outer part of the curved portion 10 a of the elbow part 10. The attachment structure will be described below in detail. The injector 5 injects only a urea aqueous solution, without mixing it with air, from an injection outlet of the tip thereof into the mixing pipe 6 towards the linear part 11. The injector 5, used in the present exemplary embodiment, has an injection angle of 25 degrees, and the center of the injection outlet of the injector 5 is positioned on a line extended from a center axis CL of the liner part 11 of the exhaust pipe 4B.

Mixing Pipe

The mixing pipe 6 is formed as a sub-unit together with a member for fixing the mixing pipe 6 to the elbow part 10 and etc. FIGS. 4 and 5 illustrate the sub-unit. It should be noted that FIG. 5 is a right side view of FIG. 4.

The mixing pipe 6 has a cylindrical shape, and the center axis thereof is coaxial to the center axis CL of the linear part 11. The mixing pipe 6 is disposed in a position within the elbow part 10 where the urea aqueous solution is injected inside from the injector 5. In other words, the mixing pipe 6 is disposed for enclosing the surrounding of the urea aqueous solution to be injected from the injector 5. The mixing pipe 6 has a plurality of openings 6 a formed on the outer peripheral surface thereof. As illustrated in FIG. 5, the plural openings 6 a are formed only in a second region B and a fourth region D, where the outer circumference of the mixing pipe 6 is equally divided into four sequentially aligned regions consisting of a first region A, the second region B, a third region C and the fourth region D at 90-degree intervals in the circumferential direction.

A first plate 15 is fixed to an upstream-side end portion (a left-side end portion in FIGS. 2 and 4), disposed on the opposite side of the outlet, of the mixing pipe 6 by means of welding. As illustrated in FIG. 5, the first plate 15 has a roughly triangle contour with a curved portion as each side thereof, and has a pipe fixation portion 15 a, an attachment portion 15 b and a guide portion 15 c. An end of the mixing pipe 6 is fixed to the pipe fixation portion 15 a by means of welding. The attachment portion 15 b is formed on the outer peripheral side of the pipe fixation portion 15 a for forming a step with the pipe fixation portion 15 a. The attachment portion 15 b is attached to the attachment portion 10 b of the elbow part 10 by means of bolts. Further, the guide portion 15 c is formed in the middle part of the pipe fixation portion 15 a, while being formed in tapered shape that the diameter thereof is reduced in proportion to distance outwardly away front the pipe fixation portion 15 a. It should be noted that the guide portion 15 c has an opening formed on an end thereof disposed on the opposite side of the pipe fixation portion 15 a.

The first plate 15 has a recessed portion 15 d formed on the opposite side of the mixing pipe 6. A second plate 16 is fixed to the recessed portion 15 d by means of welding while being fitted therein. The second plate 16 is formed in a disc shape and has an aperture 16 a, in which the injection outlet of the injector 5 is disposed, in the middle part thereof. Further, the second plate 16 has a plurality of screw apertures 16 b, and the injector 5 is supported by the second plate 16 through the screw apertures 16 b.

Inner Pipe

As illustrated in FIGS. 2 and 3, the inner pipe 7 is finned in a cylindrical shape, the outer peripheral surface thereof is supported by the tips of the support protrusions 12 c of the flange 12, and these are welded and fixed to each other. Accordingly, the inner pipe 7 is disposed at an interval away from the inner wall of the linear part 11 on the downstream side of the mixing pipe 6. In other words, a double nested pipe is formed by the inner pipe 7 and the linear part 11. Further, the inner pipe 7 has an inner diameter greater than the outer diameter of the mixing pipe 6. The inner pipe 7 is disposed at a predetermined distance away from the outlet of the mixing pipe 6.

It should be noted that the inner pipe 7 does not have any opening, slit and etc. formed on the outer peripheral surface thereof. Therefore, the exhaust gas does not flow between the outer periphery and the inner periphery of the inner pipe 7.

Arrangement of Respective Structural Members

Using FIG. 6, the positional relations among the injector 5 (an injection angle of the urea aqueous solution), the mixing pipe 6, the inner pipe 7, the exhaust pipe 4B including the elbow part 10 and the linear part 11 will be explained in detail. As described above, the mixing pipe 6 and the inner pipe 7 are herein disposed on the same axis. The injection outlet of the injector 5 is positioned on a line extended from the center axis CL of these members, while being opposed to an inlet-portion opening of the inner pipe 7.

First, an interval exists between the outlet portion (the downstream-side end portion that corresponds to the right-side end portion in FIG. 6) of the mixing pipe 6 and the inner wall of the elbow part 10. The mixing pipe 6 is supported only at an end portion thereof disposed on the opposite side of the outlet portion thereof by the elbow part 10. Therefore, no member for supporting the mixing pipe 6 is disposed in the space. In other words, an annular flow section 20 is formed that there exists no member or the like obstructing the flow of the exhaust gas. Therefore, through the flow section 20, the exhaust gas, flowing thereto from the upstream side, can flow towards the inner pipe 7 without flowing through the inside of the mixing pipe 6.

Further, a predetermined interval L is produced in a y-direction between the outlet portion of the mixing pipe 6 and the inlet portion of the inner pipe 7. In addition, the inlet portion of the inner pipe 7 has an inner diameter di greater than an inner diameter dm of the outlet portion of the mixing pipe 6.

With the aforementioned arrangement and dimensional relations, an injection angular range of the injector 5 (a range inside an angle α (25 degrees in the present exemplary embodiment) in FIG. 6) is set to be narrower than the outlet-portion opening of the mixing pipe 6 and the inlet-portion opening of the inner pipe 7. In other words, the outlet-portion opening of the mixing pipe 6 and the inlet-portion opening of the inner pipe 7 encompass the injection angular range of the injector 5.

Actions

During the activation of the engine, the exhaust gas is discharged to the exhaust pipe through the exhaust manifold. The exhaust gas flows towards the elbow part 10. As depicted with arrows G1 in FIG. 7, the exhaust gas, flowing into the elbow part 10, flows through the openings 6a of the outer peripheral surface of the mixing pipe 6 and flows into the mixing pipe 6. Further, as depicted with arrows G2 in FIG. 7, the exhaust gas flows through the flow section 20 formed between the outer peripheral surface of the mixing pipe 6 and the inner wall of the elbow part 10 and is directed to the inner pipe 7.

On the other hand, the urea aqueous solution is injected from the injector 5 towards the inside of the mixing pipe 6. The urea aqueous solution is herein injected within a range of 25 degrees about the center axis of the mixing pipe 6.

The exhaust gas from the upstream side herein flows towards the region to which the urea aqueous solution is injected. However, the urea aqueous solution is injected towards the inside of the mixing pipe 6, whereas the exhaust gas flows into the mixing pipe 6 through the openings 6 a of the mixing pipe 6. The injected urea aqueous solution is thereby less affected by the exhaust gas. Therefore, the urea aqueous solution is inhibited from attaching to the inner wall (especially, a region 10 e in FIG. 7) of the elbow part 10 opposed to the mixing pipe 6.

Further, when flowing into the mixing pipe 6 through the openings 6 a of the mixing pipe 6, the exhaust gas, flowing through the openings 6 a, forms a helical flow inside the mixing pipe 6 as illustrated in FIG. 8 due to the openings 6 formed only in the second region B and the fourth region D. The helical flow of the exhaust gas is supposed to promote the mixture of the exhaust gas and the urea aqueous solution and promotes the miniaturization of the urea aqueous solution.

As described above, the exhaust gas to which the urea aqueous solution is added in the mixing pipe 6 and the exhaust gas having flown through the flow section 20 flow into the inner pipe 7. The exhaust gas, having flown through the flow section 20, mainly flows downstream through the outer periphery of the inner pipe 7, i.e., the space between the outer peripheral surface of the inner pipe 7 and the inner wall of the exhaust pipe 4B. The inner pipe 7 is thereby heated. Further, inside the inner pipe 7, the urea aqueous solution is hydrolyzed and changed into ammonia by means of the heat of the exhaust gas and the water vapor in the exhaust gas.

The urea aqueous solution is herein attached to the inner wall of the inner pipe 7. However, as described above, the inner pipe 7 is being heated by means of the exhaust gas flowing through the outer periphery thereof. Therefore, chemical reactions are promoted and the urea aqueous solution is inhibited from attaching to the inner pipe 7.

The ammonia, produced as described above, is supplied together with the exhaust gas to the SCR. Then, the ammonia is used as a reducing agent in the reducing catalyst unit and nitrogen oxide in the exhaust gas is reduced and purified.

Features

(1) The urea aqueous solution is injected into the mixing pipe 6, whereas the exhaust gas flows into the mixing pipe 6 through the openings 6 a of the mixing pipe 6. Therefore, the urea aqueous solution is inhibited from attaching to the inner wall of the elbow part 10.

(2) The openings 6a are formed only in a partial region of the outer peripheral surface of the mixing pipe 6. Therefore, the exhaust gas, having flown into the mixing pipe 6 through the openings 6 a, becomes the helical flow. The helical flow of the exhaust gas well disperses the urea aqueous solution injected from the injector 5 and miniaturization thereof is promoted inside the mixing pipe. Therefore, the exhaust gas and the urea aqueous solution are uniformly mixed.

(3) The exhaust gas, to which the urea aqueous solution is added, flows through the inner pipe 7 heated by the exhaust gas. Therefore, the urea aqueous solution can be inhibited from attaching and accumulating onto the inner wall of the inner pipe 7.

(4) The flow section 20 is formed on the outer periphery of the outlet portion of the mixing pipe 6. The exhaust gas, having flown from the upstream side, flows into the mixing pipe 6, while flowing through the flow section 20 and being directed to the inner pipe 7. Therefore, the flow path resistance in the exhaust gas is reduced within the exhaust pipe 4B and the back pressure of the engine is inhibited.

(5) The mixing pipe 6 is supported only at the end portion thereof disposed on the opposite side of the outlet portion thereof by the elbow part 10. No member or the like her obstructing the flow of the exhaust gas exists in the flow section 20 on the outer periphery of the outlet portion. Therefore, the flow path resistance can be further reduced within the exhaust pipe 4B.

(6) A predetermined interval is produced between the outlet portion of the mixing pipe 6 and the inlet portion of the inner pipe 7 in the direction arranged along the exhaust stream, and the inlet portion of the inner pipe 7 has a diameter greater than that of the outlet portion of the mixing pipe 6. Further, the outlet-portion opening of the mixing pipe 6 and the inlet-portion opening of the inner pipe 7 encompass the injection angular range of the urea aqueous solution to be injected from the injector 5. Therefore, the exhaust gas easily flows into the inner pipe 7, and in addition, the urea aqueous solution injected hum the injector 5 is prevented from directly colliding against the inner wall of the mixing pipe 6. Further, the injected urea aqueous solution can be efficiently inhaled inside the inner pipe 7.

Other Exemplary Embodiments

The present invention is not limited to the aforementioned exemplary embodiment, and a variety of changes or modifications can be herein made without departing from the scope of the present invention.

(a) FIG. 9 illustrates another exemplary embodiment. In the exemplary embodiment illustrated in FIG. 9, the inner pipe and the support structure thereof, and the connection structure between the elbow part and the linear part of the exhaust pipe are different from those of the aforementioned exemplary embodiment, while the other configurations are similar to those of the aforementioned exemplary embodiment.

An exhaust pipe 24 in the present exemplary embodiment is formed by an elbow part 25 and a linear part 26.

The connection portion of the elbow part 25 to the linear part 26 is different from that of the elbow part 10 of the aforementioned exemplary embodiment, but the other configurations of the elbow part 25 are similar to those of the elbow part 10. The linear part 26 has a flanged portion 26 a with a diameter increased upstream on the upstream-side end portion thereof. The elbow part 25 is provided with a flange unit 27, formed by an annular member and a gasket, on the downstream-side end portion thereof. Further, the flanged portion 26 a of the linear part 26 is coupled to the flange unit 27 of the elbow part 25. Yet further, the linear part 26 has four support recessed portions 26 b, recessed to the inner peripheral side, on a roughly intermediate portion thereof in the longitudinal direction along the exhaust stream.

An inner pipe 30 has a cylindrical shape and makes contact with the four support recessed portions 26 b at the outer peripheral surface of the roughly intermediate part thereof in the longitudinal direction. Further, the outer peripheral surface of the outlet-side end portion of the inner pipe 30 is supported by the linear part 26 through an annular support member 31. The support member 31 is fixed to the outer peripheral surface of the outlet-side end portion of the inner pipe 30 by means of spot welding. Therefore, the support member 31 restricts the flow of the exhaust gas flowing through the outer periphery of the inner pipe 30. It should be noted that the term “restrict” herein includes a case of blocking all the exhaust gas flowing through the outer periphery of the inner pipe 30 and a case of allowing a small amount of the exhaust gas to flow therethrough.

Further, the inner pipe 30 has openings 30 a on the outlet-side end portion thereof across a predetermined upstream-side range except far the region on which the support member 31 is disposed.

In such exemplary embodiment, the exhaust gas, flowing through the outer periphery of the inner pipe 30, heats the inner pipe 30 and then the flow thereof is restricted by the support member 31. Further, the exhaust gas, blocked by the support member 31, is directed inside the inner pipe 30 through the openings 30 a of the inner pipe 30. Then, the exhaust gas is again mixed with the urea aqueous solution at the outlet portion of the inner pipe 30.

In such exemplary embodiment, the exhaust gas and the urea aqueous solution can be more efficiently mixed, in addition to advantageous effects similar to those of the aforementioned exemplary embodiment.

(b) The shape of the mixing pipe and the region in Which openings are formed are not limited to those of the aforementioned exemplary embodiment.

For example, as illustrated in FIG. 10, a mixing pipe 6′ may have such a tapered shape with a diameter increased downstream in the injection direction. In this case, the urea aqueous solution injected from the injector 5 can be inhibited from attaching to the inner wall of the mixing pipe 6′.

Further in the aforementioned exemplary embodiment, as illustrated in FIG. 5, the openings 6 a are formed in the second region B and the fourth region D of the mixing pipe 6. However, openings may be formed in the first region A and the third region C, which are opposed to (facing) each other. Further, openings may be formed only in one of the four regions. Each region in which openings are famed is not limited to a 90-degree range. For example, openings may be formed in a region with an angular range of either less than 90 degrees or greater than 90 degrees. (c) In the aforementioned exemplary embodiment, the urea aqueous solution has been used as a reducing agent. However, the present invention can be similarly applied even when another reducing agent is used.

According to the reducing agent aqueous solution mixing device of the illustrated embodiments, it is possible to efficiently direct the reducing agent aqueous solution injected from the injector to the inner pipe, and further, to inhibit the reducing agent aqueous solution from attaching to the inner wall of an injector attached portion of the exhaust pipe. 

The invention claimed is:
 1. A reducing agent aqueous solution mixing device for adding a reducing agent aqueous solution to an exhaust gas, the reducing agent aqueous solution mixing device being adapted to be disposed between a filter for trapping particulate substance in the exhaust gas and a reducing catalyst unit for reducing and purifying nitrogen oxide in the exhaust gas, the reducing agent aqueous solution mixing device comprising: an exhaust pipe including an elbow part having a curved portion, and a linear part disposed on an exhaust downstream side of the elbow part; an injector disposed outside the curved portion of the elbow part, the injector being configured to inject only the reducing agent aqueous solution in an air unmixed state into the elbow part towards the linear part; an inner pipe disposed on an exhaust downstream side of the injector with an exhaust upstream side inlet portion opening of the inner pipe facing the injector and an outer peripheral surface of the inner pipe being spaced apart from an inner wall of the exhaust pipe in the linear part, the inner pipe being configured to allow the exhaust gas to flow through an inside thereof and along at least a majority of an outer periphery thereof in an exhaust flow direction; and a tubular guide member provided in the elbow part as a separate member from the inner pipe and configured to direct the reducing agent aqueous solution injected from the injector to the inner pipe, the tubular guide member being arranged spaced apart from the exhaust upstream side of the exhaust upstream side inlet portion opening of the inner pipe such that a path exists between the tubular guide and the inner pipe for exhaust gas to flow into the exhaust upstream side inlet portion opening of the inner pipe without passing through the tubular guide.
 2. The reducing agent aqueous solution mixing device recited in claim 1, wherein the guide member is a mixing pipe arranged to enclose a surrounding of the reducing agent aqueous solution injected from the injector, the mixing pipe having a plurality of openings on an outer peripheral surface thereof.
 3. The reducing agent aqueous solution mixing device recited in claim 2, wherein an exhaust downstream side outlet portion of the mixing pipe is spaced apart from the inner wall of the exhaust pipe, and a flow section is formed between the outlet portion of the mixing pipe and the inner wall of the exhaust pipe in order to direct the exhaust gas from an outer periphery of the mixing pipe to the inner pipe.
 4. The reducing agent aqueous solution mixing device recited in claim 3, wherein the mixing pipe is supported at an end portion thereof disposed oppositely to the outlet portion by an elbow part wall facing the linear part.
 5. The reducing agent aqueous solution mixing device recited in claim 2, wherein the openings of the mixing pipe are formed only in a partial angular range of the mixing pipe in a circumferential direction.
 6. The reducing agent aqueous solution mixing device recited in claim 5, wherein the openings of the mixing pipe are formed either only in first and third regions or in second and fourth regions where an outer circumference of the mixing pipe is equally divided in four sequentially aligned regions consisting of the first region, the second region, the third region and the fourth region at 90-degree intervals in the circumferential direction.
 7. The reducing agent aqueous solution mixing device recited in claim 2, wherein an inlet portion of the inner pipe has an inner diameter greater than an inner diameter of the outlet portion of the mixing pipe.
 8. The reducing agent aqueous solution mixing device recited in claim 7, wherein the mixing pipe and the inner pipe are disposed so that an outlet portion opening of the mixing pipe and the inlet portion opening of the inner pipe encompass an injection angular range of the injector.
 9. The reducing agent aqueous solution mixing device recited claim 2, wherein the mixing pipe and the inner pipe are coaxially disposed.
 10. The reducing agent aqueous solution mixing device recited in claim 1, further comprising: a support member including support portions supporting a plurality of circumferential portions of an outer peripheral part of the inner pipe with respect to the exhaust pipe at a single position in a direction along an exhaust stream so that the exhaust gas flows through regions between the support member and an outer peripheral surface of the inner pipe except for regions where the support portions are provided, wherein the inner pipe has no opening formed on the outer peripheral surface thereof.
 11. The reducing agent aqueous solution mixing device recited in claim 1, further comprising: a support member supporting an outlet portion of the inner pipe with respect to the exhaust pipe, the support member being configured to restrict a flow of the exhaust gas in a region between the outer peripheral surface of the inner pipe and the inner wall of the exhaust pipe, wherein the outlet portion of the inner pipe has a plurality of openings formed on an outer peripheral surface thereof.
 12. An exhaust gas post-treatment device comprising: a filter configured to trap particulate substance in an exhaust gas; and the reducing agent aqueous solution mixing device recited in claim 1 disposed parallel to the filter on an exhaust downstream side of the filter, the reducing catalyst unit being disposed on the exhaust downstream side of the reducing agent aqueous solution mixing device, the reducing catalyst unit being configured to reduce and purify nitrogen oxide in the exhaust gas.
 13. The exhaust gas post-treatment device recited in claim 12, wherein the reducing catalyst unit is disposed parallel to the reducing agent aqueous solution mixing device.
 14. The exhaust gas post-treatment device recited in claim 12, wherein the exhaust pipe of the reducing agent aqueous solution mixing device has a cylindrical shape, with an exhaust upstream side end of the exhaust pipe being connected to the filter and an exhaust downstream side end of the exhaust pipe being connected to the reducing catalyst unit.
 15. The reducing agent aqueous solution mixing device recited in claim 1, wherein the linear part of the exhaust pipe and the inner pipe are cylindrical in shape and arranged coaxially with respect to one another.
 16. The reducing agent aqueous solution mixing device recited in claim 15, further comprising: a flange that supports the inner pipe inside the exhaust pipe, the flange being configured and arranged to surround a portion of the outer periphery of the inner pipe, the flange including at least one aperture arranged between the outer periphery of the inner pipe and an inner periphery of the exhaust pipe.
 17. The reducing agent aqueous solution mixing device recited in claim 1, wherein a predetermined interval exists between an outlet portion of the guide member and the inlet portion of the inner pipe along an axial direction of the linear part.
 18. A reducing agent aqueous solution mixing device for adding a reducing agent aqueous solution to an exhaust gas, the reducing agent aqueous solution mixing device being adapted to be disposed between a filter for trapping particulate substance in the exhaust gas and a reducing catalyst unit for reducing and purifying nitrogen oxide in the exhaust gas, the reducing agent aqueous solution mixing device comprising: an exhaust pipe including an elbow part having a curved portion, and a linear part disposed on an exhaust downstream side of the elbow part; an injector configured to inject only the reducing agent aqueous solution in an air unmixed state into the elbow part towards the linear part; an inner pipe disposed on an exhaust downstream side of the injector with an exhaust upstream side inlet portion opening of the inner pipe facing the injector and an outer peripheral surface of the inner pipe being spaced apart from an inner wall of the exhaust pipe in the linear part, the inner pipe having an exhaust upstream inlet opening and an exhaust downstream outlet opening, the inner pipe having an outer peripheral surface being spaced inward apart from an inner wall of the linear part to define a bypass passageway for a first portion of the exhaust gas to flow through an inside the inner pipe and a second portion of the exhaust gas to flow along the outer peripheral surface of the inner pipe in a space between the inner wall of the linear part; and a tubular guide member provided in the elbow part as a separate member from the inner pipe and configured to direct the reducing agent aqueous solution injected from the injector to the inner pipe, the tubular guide member being arranged spaced apart from the exhaust upstream side of the exhaust upstream side inlet portion opening of the inner pipe such that a path exists between the tubular guide and the inner pipe for exhaust gas to flow into the exhaust upstream side inlet portion opening of the inner pipe without passing through the tubular guide. 